Avocados are berries which have a pear shape. They may also be known as butter fruits or alligator pears due to the scaly or leathery appearance many varieties of avocados have. It is believed that avocados were first cultivated by humans around 8000 BC in South and Central America. Mexico is currently the largest producer of these fruits, with Brazil, the United States and Columbia following.
Many varieties of avocados begin a dark green color and turn black as they ripen. The flesh of the avocado is a yellowish-green, has a buttery consistency and a nutty flavor. Hass is a typically brown avocados. Fuerte avocados have a smoother dark green skin and are larger than the Hass. Zutano and Bacon varieties are also available, though they are less common.
Avocados contain several valuable nutrients such as vitamins A, B6, C, E and K. They also contain high amounts of calcium, copper, foliate, magnesium and potassium along with plenty of fiber. Avocados have a high fat content, with fat accounting for 70-80 percent of the calories of the fruit. However, as much as two thirds of this fat is mono-unsaturated, a type of fat that is beneficial to your overall health.
If the avocado you have is not Hass, an avocado may turn brown because it has been handled harshly and has become bruised. This causes the inside and outside to take on a brownish hue. When you cut an avocado, this will expose the flesh to oxygen. As the flesh oxidizes, it will start to brown as well. If your avocado is slightly browned, you can still eat it, but the flavor may be bitterer than a fresher avocado would be. However, if your avocado's flesh has become very dark or the flesh has become stringy, you should avoid eating it, particularly if there is any sign of mold. Avocados have a very high fat content, so they oxidize and become rancid very quickly at room temperature and will need to be thrown away.
In general, reducing the avocado's exposure to the air will help you keep it fresh for a longer period of time.